An apparatus of this kind in the design as a blast convection furnace for heating glass panes fed by means of rollers is known from DE-PS 40 10 280. For a single chamber furnace, or a zone of a multi-zone furnace, this design provides radial blowers in a strictly spatially symmetrical arrangement in order to achieve a very even temperature distribution in the treatment gas flow by means of a strictly symmetric guiding of the flow. However, this aim is achieved by means of a great technical effort, i.e. four radial blowers are required for each single chamber furnace or for each zone of a multi-zoned furnace.
On account of the relatively small intake cross-section of a radial ventilator, the treatment gas is suctioned in a relatively pointed manner out of the interior of the treatment space, which results in relatively large irregularities in the flow out of the interior space so that an even temperature distribution is not strictly ensured even in the case of this elaborate concept.
The required large volume flows of treatment gas, even in the case of four fans per single chamber furnace, or per zone of a multi-zoned furnace, demand such a large rotor outer diameter for each individual radial fan --and thus a correspondingly large structural height of the ventilator together with the fan housing--that in many cases, the desired operation height of approximately 1200 mm cannot be met, or an expensive pit is required for the furnace.
Further, the guidance of the flow of the treatment gas is still angled--together with correspondingly high pressure losses--as the treatment gas must be deflected about 90.degree. when the treatment gas flows into the ejector ribs.
The use of cross-flow fans is already known for numerous applications, even for heating air. However, any advantages from cross-flow fans built into convection heaters for flat glass have been overlooked. Apparently, this is based on prejudices, for example on account of the high heating gas temperatures between 600.degree. and 700.degree. C. which are necessary for heating the flat glass, since the centrifugal loads on the rotating components that are very large for a cross-flow fan are only barely coped with at such temperatures.
Proceeding on the basis of the prior art according to the initially described DE-PS 40 10 280, it is the object of the invention to avoid the disadvantages of this known design and to provide a convection heater or cooler for flat glass operating with a uniform temperature distribution of a treatment gas flow with simple technical means.